In the manufacture of MEMS elements having mechanical element parts such as sensors and actuators integrated on substrates, the predominant portion is processed using the semiconductor integrated circuit fabrication technology. For forming movable structure parts and stereo-structure parts, the MEMS technology utilizes inherent processing techniques such as sacrificial layer etching technique, deep drilling/etching technique, and anisotropic etching technique. Among these techniques, the sacrificial layer etching technique is an important technique involving depositing a plurality of layers on a substrate, and selectively removing the lower layer called sacrificial layer, leaving the upper layer. With respect to the materials used in the sacrificial layer, many reports have been made. For example, JP-A 2000-255072 discloses a positive novolak resist composition which can be advantageously processed to form fine size features, but has poor heat resistance, by which a choice of the material of the upper layer is limited.
As a solution to this problem, one approach proposed thus far is by providing a positive resist composition based on a cresol novolak resin and adding a crosslinker thereto, followed by certain steps. Although this approach enables relatively fine size processing and offers sufficient heat resistance, it has poor sensitivity and fails to reach a target resolution estimated in the future.